I would be wary about anything past 1 GPU, not only because of the added block, but mostly the added radiators. Putting 3 or 4 cards under water is gonna want more radiator space. I have a 980Ti and a 6700K and a 3X140 radiator, and it puts out some warmth when I'm gaming. I have an EK D5 PWM pump in mine, and the Swiftech pump is rated at just about half the pressure, and a little over a third l/hr, that's not necessarily a bad thing. You need the water in the radiator long enough for it to get the heat out, but more stuff needs more water and more radiator.